Transfer no audio issues

I'm new to this forum, however, as far as I can tell, I searched everything, but can't find an explanation for my problem.

I've got a 3CX v11 server (SP4) running on a server Widnows 2008R2. Server is connected directly to the internet, no firewall in between. Obivously Windows Firewall is enabled, however all needed ports are configured. I've got a strange problem, I can't determine the cause...

We're using Cisco SPA514G phones on a remote location (behind a simple Engenius router), and all appears fine. We can make internal calls, outgoing calls, incoming works like a charm, we can transfer internally, however....

We've got an issue with transferring external calls... We've got the Cisco's configured with two Transfer options. One "Blind", one "normal". We've got an issue with external-party-1, local-phone and external-party-2.
The Blind Transfer works... External call comes in, we answer it via "pick-up" or directly. Audio is fine. Hit the "BXFR" key, input another external number, dial, and call is transferred, including audio.
"Normal" Transfer fails.. External call comes in, we answer it via "pick-up" or directly. Audio is fine. Hit the "XFR" key, input another external number, dial, and call connected, audio is fine. However, when we xfer the call, call is connected, but there is NO audio!

As I'm not that into voice, can somebody give me any insight into what could be wrong? Everything appears OK, however, no audio between the two external parties.

I've experimented with the "PBX delivers audio", Support Re-Invite, Support Re-Place, none appear to be helping... I've got log files of both occurences, if that helps??? (have to anonymise it obviously )

...and after having completed these changes repeat the test and advise the outcome. If this does not help, something nasty is happening involving NAT traversal, an investigation into a Wireshark capture will be necessary.

Kevin Attard Compagno
Technical Support Manager
http://www.3cx.com

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